Barack Obama today received his first classified intelligence briefing from the CIA, lesson one in a 75-day crash course in how to be a US President.

Such sessions, which typically last 45 minutes to an hour, are among the most visible parts of the transition from victorious candidate to president, along with increased Secret Service Detail. Other aspects of the autumn ritual of presidential transitions, like the requisite meeting between the President-elect and the outgoing leader, are also underway.

Bush has invited Obama to the White House next Monday. Protocol dictates that Laura Bush and Michelle Obama will retire to the living quarters for a White House tour.

But the biggest challenge in the transition from winning candidate to president-elect will be deciding how he wants to run his administration, and what items to put on the top of his agenda from his long list of campaign promises.

This is decision time for Obama: does he want a free-wheeling White House with young aides ordering pizza at all hours of the day and night like Bill Clinton? Or does he want to live life in 15-minute increments like the rigidly scheduled White House of George Bush?

"Presidential decision making is not a bunch of guys sitting around a table. It's much more complex than that," said John P Burke, a politics professor at the University of Vermont who specialises in presidential transitions.

"There has to be an awareness of the importance of an effective decision making process that precedes the policy choices that the president himself will have to make."

Early indications are that Obama wants a more disciplined and buttoned down White House than Clinton.

The last Democratic president, overly focused on his cabinet appointments, squandered previous time by not a White House chief of staff until a month before his first term started.

Obama, who has had his transition team quietly working for months, named Rahm Emanuel as his chief of staff today.

"They are probably going to be off to a faster start than just about any transition team in memory," said Roy Neel, who was involved in the Clinton transition and headed Al Gore's transition team. "They have done an awful lot of pre-election work."

Such decisions are more than a matter of style. Unlike cabinet appointments, White House staff do not need to undergo Senate confirmation hearings. Emanuel and his team can get down to work right away.

Senate confirmation proceedings for cabinet posts will only get under way in January. The business of confirming about 500 sub-cabinet posts is far more laborious.

Obama probably will not get all of his people in place until September 2009 and the process will likely take even longer for political jobs further down the list like ambassadorships and board appointments.

Meanwhile, Emanuel can get to work on what amounts to a huge personnel exercise: staffing the 500 or so political posts in the White House and executive office.

About 1,000 other people, employed fulltime at the White House, are professional staff and will stay on after Bush.

The next big task awaiting Obama is to decide which among his many campaign promises will be top of the agenda in his Administration. Part of that decision will be made in the next round of meetings Obama faces.

On the ceremonial side, there will be phone calls and visits with foreign leaders.

Obama will also hold separate meetings with the Democratic and Republican leaderships in the Senate. "Those are not necessarily courtesies. The meetings with congressional leader will be nuts and bolts -- working sessions as well as ceremonial," said Roy Neel, who was involved with the Clinton transition and headed Al Gore's transition team.

"They will talk about how they will work, what president-elect Obama wants to do and what the Democratic leadership in Congress wants to do to establish a productive working relationship so that they can get all these things done very quickly."

All presidents are under pressure to use the coming 74 days to get off the ground running. For Obama, though, who came to power promising hope and change, establishing his priorities and putting together an effective team, is even more critical.

"The bottom line is that presidents need to prioritise but this president is really going to have to prioritise," said Burke.